Are individual indexes necessary on columns that are included in a compound primary key?

I have this M2M join table:

CREATE TABLE [dbo].[RecipientsDonors]
(
  [RecipientId] [int] NOT NULL,
  [DonorId] [int] NOT NULL,
  CONSTRAINT [PK_RecipientsDonors] PRIMARY KEY CLUSTERED 
  (
    [RecipientId] ASC,
    [DonorId] ASC
  )
)

I also have these two indexes:

CREATE NONCLUSTERED INDEX [IX_RecipientsDonors_RecipientId] ON [dbo].[RecipientsDonors]
(
  [RecipientId] ASC
)

CREATE NONCLUSTERED INDEX [IX_RecipientsDonors_DonorId] ON [dbo].[RecipientsDonors]
(
  [DonorId] ASC
)

My intent with the two indexes is to speed single-column lookups. Given the existence of the primary key, are the indexes redundant? Or instead are they necessary because the primary key includes both columns?